By the old production methods, hose with thread reinforcing was built up on a core which carried and supported the successively applied material layers. With this method it was possible to produce only disconnected lengths of hose up to a length of perhaps 40 meters. The cores were in part hard and in part elastically flexible so that the hose could be wound on a drum for vulcanization. Both kinds of cores had their advantages and disadvantages. The removal of the long cores after vulcanization could be done only with difficulty and effort as well as considerable expense.
It has been known for many years to produce continuous rubber hose with textile thread inlays without use of a core. Such production even today entails considerable difficulty. By reason of these difficulties it is often not possible to use the desired materials but rather more expensive materials, the properties of which are often less favorable for the use of the hose. These materials have however the property that they facilitate the production of the hose. Likewise, it is not possible to use any desired textile thread with the particular rubber material being used. For the textile thread inlay there are the possibilities of applying a layer of textile thread to the inner rubber tube extruded by the first extruder by weaving or knitting. Other possibilities are merely to wind the thread around the inner extruded tube either crosswise with threads wound in one direction passing alternately under and over threads wound in the other direction or simply with two crosswise layers wound one over the other. The latter possibility lends itself to high speed production. However, such high speed production though possible in the application of the textile thread and in the extrusion of the hose by screw type extruders cannot in practice be attained or can be attained only with difficulties since the required vulcanization apparatus for such high rate of production must be extremely long because of the need of subjecting the hose to a certain vulcanization time.
For the vulcanization it is known to use hot baths, in particular salt baths. It is also known to effect vulcanization by the use of UHF energy. The installation used for this purpose uses hollow conductors which are fed with electromagnetic waves of a wavelength in the centimeter or decimeter range. Fluid bed vulcanization apparatus has heretofore been used in the production of hose.
The carrying out of the vulcanization of rubber hose with textile thread inserts in salt baths or in fluid bed apparatus requires an installation of great length. The use exclusively of UHF energy for vulcanization is not desirable. It is expensive and has the disadvantage that individual places on tubes of considerable wall thickness are frequently heated to too high a temperature so as to cause burning. For this reason several successive UHF vulcanization apparatuses can be used with hot air stretches between them. This also leads to a long installation and considerable expense for the vulcanization equipment.
It has been proposed to shorten the vulcanization time considerably by applying a UHF field to the hose to be vulcanized in such manner that the UHF energy is preferably absorbed by the inner material layer and then the outer temperature during the time of vulcanization can be held at a proper value for vulcanization. In this manner it is possible to produce rubber hose with textile thread inserts with a relatively short vulcanization and obtain outstanding quality. However, it is necessary that a polyester thread be used and that the inner material have a stronger polarity than the material of the outer layer.